A blood pressure is one index for analyzing a cardiovascular disease. Performing risk analysis of the cardiovascular disease based on the blood pressure is effective in preventing cardiovascular diseases such as apoplexy, cardiac arrest, cardiac infarct and the like. Among them, an early morning high blood pressure, in which the blood pressure rises early in the morning is related to heart disease, apoplexy, and the like. Furthermore, a symptom of the early morning high blood pressure called the morning surge in which the blood pressure suddenly rises between one hour and one and a half hour after waking up is known to have a causal connection with apoplexy.
Therefore, it is useful in the risk analysis of the cardiovascular disease to grasp a mutual relationship of time (lifestyle habit) and change in blood pressure. The blood pressure thus needs to be continuously measured over a long period of time.
When monitoring a patient during surgery and after surgery, or when checking an effect of medicine at the time of antihypertensive treatment, and the like, it is very important to measure the blood pressure continuously for every heart beat, and to monitor the change in blood pressure. A blood pressure waveform for every heart beat contains information that is of a very wide medical usage range such as advancement in arterial sclerosis, and diagnosis of heart function. It is thus also important to continuously record the fluctuation of the blood pressure waveform.
Japanese Unexamined Patent Publication No. 54-50175 (Patent Document 1) describes a sphygmomanometer that uses a volume compensation method as a technique for measuring the blood pressure for every heart beat. The volume compensation method is as follows. An artery is compressed by a cuff from outside a living body, and a volume (volume per unit length) of the artery that pulsates in synchronization with the heart beat is maintained constant on a steady basis. The pressure (cuff pressure) at which a measurement site is compressed and an inner pressure, that is, the blood pressure of the artery or the measurement site are made equilibrium by maintaining the volume of the artery constant. The cuff pressure when this equilibrium state is maintained is detected to continuously obtain the blood pressure value.
Patent Document 1: Japanese Unexamined Patent Publication No. 54-50175